Transverse and longitudinal Bose-Einstein correlations in hadronic Z $^0$ decays

Abstract

Bose-Einstein correlations in pairs of identical charged pions produced in a sample of 4.3 million Z 0 hadronic decays are studied as a function of the three components of the momentum difference, transverse ("out" and "side") and longitudinal with respect to the thrust direction of the event. A significant difference between the transverse, r t side , and longitudinal, r l , dimensions is observed, indicating that the emitting source of identical pions, as observed in the Longitudinally CoMoving System, has an elongated shape. This is observed with a variety of selection techniques. Specifically, the values of the parameters obtained by fitting the extended Goldhaber parametrisation to the correlation function C ′ = C DATA /C MC for two-jet events, selected with the Durham algorithm and resolution parameter y cut = 0.04, are r t side = (0.809 ± 0.009 (stat) +0.019 −0.032 (syst)) fm, r l = (0.989 ± 0.011 (stat) +0.030 −0.015 (syst)) fm and r l /r t side = 1.222 ± 0.027 (stat) +0.075 −0.012 (syst). The results are discussed in the context of a recent model of Bose-Einstein correlations based on string fragmentation.

Bose Einstein and Fermi Dirac interferometry in particle physics

“…where r z , estimated from equation (22) as Q z approaches zero, is the longitudinal geometrical radius and r T is composed of the transverse radius and the emission time difference. The experimental findings in heavy-ion collisions [33,34], in hadron-hadron reactions [35,36] and e + e − annihilations [37][38][39], verify the theoretical expectations of the Lund string model [40,41] that the ratio r T /r z is significantly smaller than one (see section 4.1.2).…”

Bose–Einstein Correlations in pp and pPb Collisions at LHCb

“…Bose-Einstein correlations were first observed in the field of elementary particle physics in 1959 [6] (Fermi-Dirac correlations slightly later) and were studied in many different collision systems and energies since then. Among others, a number of analyses were conducted for e + e − collisions at LEP [7][8][9][10][11][12][13][14] and for pp collisions at LHC by collaborations: ALICE, ATLAS and CMS [15][16][17][18][19]. BEC measurements were also done for heavy ion collisions, e.g., by ALICE [20] and STAR [21].…”